/*
 *
 * (c) Copyright Ascensio System Limited 2010-2018
 *
 * This program is freeware. You can redistribute it and/or modify it under the terms of the GNU 
 * General Public License (GPL) version 3 as published by the Free Software Foundation (https://www.gnu.org/copyleft/gpl.html). 
 * In accordance with Section 7(a) of the GNU GPL its Section 15 shall be amended to the effect that 
 * Ascensio System SIA expressly excludes the warranty of non-infringement of any third-party rights.
 *
 * THIS PROGRAM IS DISTRIBUTED WITHOUT ANY WARRANTY; WITHOUT EVEN THE IMPLIED WARRANTY OF MERCHANTABILITY OR
 * FITNESS FOR A PARTICULAR PURPOSE. For more details, see GNU GPL at https://www.gnu.org/copyleft/gpl.html
 *
 * You can contact Ascensio System SIA by email at sales@onlyoffice.com
 *
 * The interactive user interfaces in modified source and object code versions of ONLYOFFICE must display 
 * Appropriate Legal Notices, as required under Section 5 of the GNU GPL version 3.
 *
 * Pursuant to Section 7 § 3(b) of the GNU GPL you must retain the original ONLYOFFICE logo which contains 
 * relevant author attributions when distributing the software. If the display of the logo in its graphic 
 * form is not reasonably feasible for technical reasons, you must include the words "Powered by ONLYOFFICE" 
 * in every copy of the program you distribute. 
 * Pursuant to Section 7 § 3(e) we decline to grant you any rights under trademark law for use of our trademarks.
 *
*/


using System;
using System.Linq;
using System.Text;

namespace ASC.Common.Utils
{
    public static class MimeHeaderUtils
    {
        public static string EncodeMime(string mimeHeaderValue)
        {
            return EncodeMime(mimeHeaderValue, Encoding.UTF8, false);
        }

        public static string EncodeMime(string mimeHeaderValue, Encoding charset, bool split)
        {
            if (MustEncode(mimeHeaderValue))
            {
                var result = new StringBuilder();
                var data = charset.GetBytes(mimeHeaderValue);
                var maxEncodedTextSize = split ? 75 - ("=?" + charset.WebName + "?" + "B"/*Base64 encode*/ + "?" + "?=").Length : int.MaxValue;

                result.Append("=?" + charset.WebName + "?B?");
                var stored = 0;
                var base64 = Convert.ToBase64String(data);
                for (var i = 0; i < base64.Length; i += 4)
                {
                    // Encoding buffer full, create new encoded-word.
                    if (stored + 4 > maxEncodedTextSize)
                    {
                        result.Append("?=\r\n =?" + charset.WebName + "?B?");
                        stored = 0;
                    }

                    result.Append(base64, i, 4);
                    stored += 4;
                }
                result.Append("?=");
                return result.ToString();
            }
            return mimeHeaderValue;
        }

        public static bool MustEncode(string text)
        {
            return !string.IsNullOrEmpty(text) && text.Any(c => c > 127);
        }
    }
}